1/*
2 * Copyright (c) 1998, 2017, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25#ifndef SHARE_VM_RUNTIME_JNIHANDLES_HPP
26#define SHARE_VM_RUNTIME_JNIHANDLES_HPP
27
28#include "memory/allocation.hpp"
29#include "runtime/handles.hpp"
30
31class JNIHandleBlock;
32
33
34// Interface for creating and resolving local/global JNI handles
35
36class JNIHandles : AllStatic {
37  friend class VMStructs;
38 private:
39  static JNIHandleBlock* _global_handles;             // First global handle block
40  static JNIHandleBlock* _weak_global_handles;        // First weak global handle block
41  static oop _deleted_handle;                         // Sentinel marking deleted handles
42
43  inline static bool is_jweak(jobject handle);
44  inline static oop& jobject_ref(jobject handle); // NOT jweak!
45  inline static oop& jweak_ref(jobject handle);
46
47  template<bool external_guard> inline static oop guard_value(oop value);
48  template<bool external_guard> inline static oop resolve_impl(jobject handle);
49  template<bool external_guard> static oop resolve_jweak(jweak handle);
50
51 public:
52  // Low tag bit in jobject used to distinguish a jweak.  jweak is
53  // type equivalent to jobject, but there are places where we need to
54  // be able to distinguish jweak values from other jobjects, and
55  // is_weak_global_handle is unsuitable for performance reasons.  To
56  // provide such a test we add weak_tag_value to the (aligned) byte
57  // address designated by the jobject to produce the corresponding
58  // jweak.  Accessing the value of a jobject must account for it
59  // being a possibly offset jweak.
60  static const uintptr_t weak_tag_size = 1;
61  static const uintptr_t weak_tag_alignment = (1u << weak_tag_size);
62  static const uintptr_t weak_tag_mask = weak_tag_alignment - 1;
63  static const int weak_tag_value = 1;
64
65  // Resolve handle into oop
66  inline static oop resolve(jobject handle);
67  // Resolve externally provided handle into oop with some guards
68  inline static oop resolve_external_guard(jobject handle);
69  // Resolve handle into oop, result guaranteed not to be null
70  inline static oop resolve_non_null(jobject handle);
71
72  // Local handles
73  static jobject make_local(oop obj);
74  static jobject make_local(JNIEnv* env, oop obj);    // Fast version when env is known
75  static jobject make_local(Thread* thread, oop obj); // Even faster version when current thread is known
76  inline static void destroy_local(jobject handle);
77
78  // Global handles
79  static jobject make_global(Handle  obj);
80  static void destroy_global(jobject handle);
81
82  // Weak global handles
83  static jobject make_weak_global(Handle obj);
84  static void destroy_weak_global(jobject handle);
85
86  // Sentinel marking deleted handles in block. Note that we cannot store NULL as
87  // the sentinel, since clearing weak global JNI refs are done by storing NULL in
88  // the handle. The handle may not be reused before destroy_weak_global is called.
89  static oop deleted_handle()   { return _deleted_handle; }
90
91  // Initialization
92  static void initialize();
93
94  // Debugging
95  static void print_on(outputStream* st);
96  static void print()           { print_on(tty); }
97  static void verify();
98  static bool is_local_handle(Thread* thread, jobject handle);
99  static bool is_frame_handle(JavaThread* thr, jobject obj);
100  static bool is_global_handle(jobject handle);
101  static bool is_weak_global_handle(jobject handle);
102  static long global_handle_memory_usage();
103  static long weak_global_handle_memory_usage();
104
105  // Garbage collection support(global handles only, local handles are traversed from thread)
106  // Traversal of regular global handles
107  static void oops_do(OopClosure* f);
108  // Traversal of weak global handles. Unreachable oops are cleared.
109  static void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
110  // Traversal of weak global handles.
111  static void weak_oops_do(OopClosure* f);
112};
113
114
115
116// JNI handle blocks holding local/global JNI handles
117
118class JNIHandleBlock : public CHeapObj<mtInternal> {
119  friend class VMStructs;
120  friend class CppInterpreter;
121
122 private:
123  enum SomeConstants {
124    block_size_in_oops  = 32                    // Number of handles per handle block
125  };
126
127  oop             _handles[block_size_in_oops]; // The handles
128  int             _top;                         // Index of next unused handle
129  JNIHandleBlock* _next;                        // Link to next block
130
131  // The following instance variables are only used by the first block in a chain.
132  // Having two types of blocks complicates the code and the space overhead in negligible.
133  JNIHandleBlock* _last;                        // Last block in use
134  JNIHandleBlock* _pop_frame_link;              // Block to restore on PopLocalFrame call
135  oop*            _free_list;                   // Handle free list
136  int             _allocate_before_rebuild;     // Number of blocks to allocate before rebuilding free list
137
138  // Check JNI, "planned capacity" for current frame (or push/ensure)
139  size_t          _planned_capacity;
140
141  #ifndef PRODUCT
142  JNIHandleBlock* _block_list_link;             // Link for list below
143  static JNIHandleBlock* _block_list;           // List of all allocated blocks (for debugging only)
144  #endif
145
146  static JNIHandleBlock* _block_free_list;      // Free list of currently unused blocks
147  static int      _blocks_allocated;            // For debugging/printing
148
149  // Fill block with bad_handle values
150  void zap();
151
152 protected:
153  // No more handles in the both the current and following blocks
154  void clear() { _top = 0; }
155
156 private:
157  // Free list computation
158  void rebuild_free_list();
159
160 public:
161  // Handle allocation
162  jobject allocate_handle(oop obj);
163
164  // Release Handle
165  void release_handle(jobject);
166
167  // Block allocation and block free list management
168  static JNIHandleBlock* allocate_block(Thread* thread = NULL);
169  static void release_block(JNIHandleBlock* block, Thread* thread = NULL);
170
171  // JNI PushLocalFrame/PopLocalFrame support
172  JNIHandleBlock* pop_frame_link() const          { return _pop_frame_link; }
173  void set_pop_frame_link(JNIHandleBlock* block)  { _pop_frame_link = block; }
174
175  // Stub generator support
176  static int top_offset_in_bytes()                { return offset_of(JNIHandleBlock, _top); }
177
178  // Garbage collection support
179  // Traversal of regular handles
180  void oops_do(OopClosure* f);
181  // Traversal of weak handles. Unreachable oops are cleared.
182  void weak_oops_do(BoolObjectClosure* is_alive, OopClosure* f);
183
184  // Checked JNI support
185  void set_planned_capacity(size_t planned_capacity) { _planned_capacity = planned_capacity; }
186  const size_t get_planned_capacity() { return _planned_capacity; }
187  const size_t get_number_of_live_handles();
188
189  // Debugging
190  bool chain_contains(jobject handle) const;    // Does this block or following blocks contain handle
191  bool contains(jobject handle) const;          // Does this block contain handle
192  int length() const;                           // Length of chain starting with this block
193  long memory_usage() const;
194  #ifndef PRODUCT
195  static bool any_contains(jobject handle);     // Does any block currently in use contain handle
196  static void print_statistics();
197  #endif
198};
199
200inline bool JNIHandles::is_jweak(jobject handle) {
201  STATIC_ASSERT(weak_tag_size == 1);
202  STATIC_ASSERT(weak_tag_value == 1);
203  return (reinterpret_cast<uintptr_t>(handle) & weak_tag_mask) != 0;
204}
205
206inline oop& JNIHandles::jobject_ref(jobject handle) {
207  assert(!is_jweak(handle), "precondition");
208  return *reinterpret_cast<oop*>(handle);
209}
210
211inline oop& JNIHandles::jweak_ref(jobject handle) {
212  assert(is_jweak(handle), "precondition");
213  char* ptr = reinterpret_cast<char*>(handle) - weak_tag_value;
214  return *reinterpret_cast<oop*>(ptr);
215}
216
217// external_guard is true if called from resolve_external_guard.
218// Treat deleted (and possibly zapped) as NULL for external_guard,
219// else as (asserted) error.
220template<bool external_guard>
221inline oop JNIHandles::guard_value(oop value) {
222  if (!external_guard) {
223    assert(value != badJNIHandle, "Pointing to zapped jni handle area");
224    assert(value != deleted_handle(), "Used a deleted global handle");
225  } else if ((value == badJNIHandle) || (value == deleted_handle())) {
226    value = NULL;
227  }
228  return value;
229}
230
231// external_guard is true if called from resolve_external_guard.
232template<bool external_guard>
233inline oop JNIHandles::resolve_impl(jobject handle) {
234  assert(handle != NULL, "precondition");
235  oop result;
236  if (is_jweak(handle)) {       // Unlikely
237    result = resolve_jweak<external_guard>(handle);
238  } else {
239    result = jobject_ref(handle);
240    // Construction of jobjects canonicalize a null value into a null
241    // jobject, so for non-jweak the pointee should never be null.
242    assert(external_guard || result != NULL,
243           "Invalid value read from jni handle");
244    result = guard_value<external_guard>(result);
245  }
246  return result;
247}
248
249inline oop JNIHandles::resolve(jobject handle) {
250  oop result = NULL;
251  if (handle != NULL) {
252    result = resolve_impl<false /* external_guard */ >(handle);
253  }
254  return result;
255}
256
257// Resolve some erroneous cases to NULL, rather than treating them as
258// possibly unchecked errors.  In particular, deleted handles are
259// treated as NULL (though a deleted and later reallocated handle
260// isn't detected).
261inline oop JNIHandles::resolve_external_guard(jobject handle) {
262  oop result = NULL;
263  if (handle != NULL) {
264    result = resolve_impl<true /* external_guard */ >(handle);
265  }
266  return result;
267}
268
269inline oop JNIHandles::resolve_non_null(jobject handle) {
270  assert(handle != NULL, "JNI handle should not be null");
271  oop result = resolve_impl<false /* external_guard */ >(handle);
272  assert(result != NULL, "NULL read from jni handle");
273  return result;
274}
275
276inline void JNIHandles::destroy_local(jobject handle) {
277  if (handle != NULL) {
278    jobject_ref(handle) = deleted_handle();
279  }
280}
281
282#endif // SHARE_VM_RUNTIME_JNIHANDLES_HPP
283